Method and system of tufting

ABSTRACT

A method and system for tufting fabrics are disclosed. In addition a number of alternative tufting heads are disclosed. The method and system take into account at least one of the following factors: the direction of traverse with respect to filaments, any change in direction of traverse, the yarn type and thickness, the orientation of the needle with respect to the filaments, the distorting effect the needle has on the filament grid network when it is inserted into the backing, and the backing. The position of the needle relative to the positions of the tufts in the pattern is adjusted in order to compensate for positional errors introduced by the factors mentioned. The tufting heads are also modified to make them suitable for automation.

TECHNICAL FIELD

This invention concerns a method of automatically tufting fabrics, and asystem for automatically tufting fabrics. In a further aspect itconcerns a tufting head mechanism.

BACKGROUND ART

Tufted carpets are commonly made by inserting tufts of wool, or otheryarns, into a backing to form a closely spaced array. A series ofneedles are used for this purpose, and each needle inserts a row oftufts into the backing as the backing is drawn away from the needle. Ifone of the needles stops tufting for some reason, for instance if theyarn breaks, then the tufting operation is not stopped but is allowed tocontinue leaving an empty row in the carpet. Subsequently a hand-heldtufting gun is used to insert the missing row of tufts.

The hand-held tufting guns developed for the repair of carpets have beenimaginatively applied to the creation of individualised carpets bearingcomplex and unusual designs; in these carpets it should be appreciatedthat the tufting is not restricted to straight rows. However, theproduction of such carpets is a highly labour intensive process andrequires great skill and flair on the part of the operator. Forinstance, the stitch length is determined by a combination of the speedat which the operator traverses the gun across the backing and the speedat which the operator drives the tufting motion of the gun. It is alsodifficult to traverse the gun accurately across the backing because theaction of the gun on the backing introduces forces which deflect theneedle.

The hand-held tufting guns include tufting head mechanisms whichtypically include a reciprocally mounted hollow needle and a yarnfeeding mechanism. There are two main types of tufting heads.

First, a purely mechanical type in which a forked rod, or narrowscissors, reciprocates within the hollow needle to drive the yarn intoposition once the backing has been parted by the needle.

Second, a pneumatic tufting head which uses a stream of compressed airflowing down through the hollow needle to entrain the yarn and drive itinto position in the backing.

Both types of tufting guns are subject to a variety of problems inoperation, such as yarn blockages, or yarn being blown back out of theneedle. These problems make the use of tufting guns difficult toautomate.

One attempt at an automated tufting gun is described in U.S. Pat. No.4,109,593. Here a pneumatic tufting gun is mounted on a carriage movablein two orthogonal directions, and the problem of maintaining the correctorientation of the needle with respect to the direction of traverse isaddressed. However, there are still a large number of problems to beovercome before such a device is able to produce an adequate product.

SUMMARY OF THE INVENTION

The present invention comprises a method of automatically tuftingfabrics in cut or loop pile, comprising the steps of:

(a) stretching a backing over a frame to form a network of filamentsextending in at least two directions;

(b) traversing a tufting head over the backing under the influence ofcontrol signals, and reciprocating a needle in the tufting head into andout of the backing at a rate related to the speed of traverse, to inserttufts of yarn into the backing in accordance with a preselected patternof tufts;

(c) taking account of one or more of the following factors:

the direction of traverse with respect to the filaments;

any change in the direction of traverse;

the yarn type and thickness;

the orientation of the needle with respect to the filaments;

the distorting effect of the (large) needle; and

the backing type; and

(d) adjusting the positions of the needle relative to the tufts in thepattern, in dependence on the factors taken into account in (c) tocompensate for errors introduced by those factors.

Adjustment of the positions of the needle relative to the tufts in thepattern can be accomplished by varying the location of the tufts in thepattern, varying the control signals, or by mechanically compensatingthe traversing and tufting head mechanisms.

The importance of compensation is that errors in tuft location in thebacking of the order, even, of a millimeter can be enough to destroy thehomogeneity of the density of the tufts, which results in a lesspleasing product. This is especially important at colour interfaceswhere any misplaced tufts can result in a fuzzy looking interface.

Preferably the method includes the step of adjusting the positions ofthe needle relative to the positions of the tufts in the pattern, independence on the distance between the position of a tuft center, andthe position where the needle tip begins to enter the backing in orderto sew that tuft.

Preferably the method includes the step of defining the pattern byvectors which represent either the length and direction of each row oftufts, or the shape and size of each area of tufts.

Preferably the method includes the step of calculating an integralnumber of tufts along the length of a line of tufts, which may becurved, from its beginning to its end.

Preferably the method includes the step of calculating an integralnumber of lines across any area.

Preferably the method includes the step of varying the spacing betweenlines on either side of, and parallel to, a boundary between two areas,within predetermined tolerances, in order to maintain line spacing atthe boundary within the predetermined tolerances.

Preferably the method includes, where an area has two taperingboundaries, the step of tufting rows in a tapered formation between thetwo boundaries to share an equal proportion of the taper between eachadjacent pair of rows.

Preferably the method includes the step of calculating an integralnumber of tufts along any given row in dependence on the spacing betweenthat row and its immediately adjacent rows in order to ensure the tuftdensity remains within predetermined upper and lower limits.

Preferably the method includes the step of displaying the pattern as adiagram showing the arranged rows of tufts, wherein the displayed rowsof tufts show their widths in scale with their lengths.

Preferably the method includes the step of checking the pattern for anyoccurrences of localised tuft density falling outside predeterminedupper and lower limits.

Preferably the method includes the step of pressing the tufting headagainst the backing during tufting at a preselected pressure to cause adesired deflection of the backing.

Preferably the method includes the step of mounting the frame onto amachine which includes means for traversing the tufting head over thebacking, before tufting, and dismounting the frame from the machine oncetufting has been completed.

The invention also concerns a system for automatically tufting fabrics,comprising:

a frame over which, in use, a backing is stretched to form a network offilaments extending in at least two directions;

traversing means to traverse a tufting head over the backing under theinfluence of control signals;

a tufting head mounted in the traversing means and having a tuftingneedle able to reciprocate into and out of the backing, at a raterelated to the speed of traverse, to insert tufts of yarn into thebacking in accordance with a preselected pattern of tufts; and

adjusting means to adjust the positions of the needle relative to thepositions of the tufts in the pattern in dependence on one or more ofthe following factors:

the direction of traverse with respect to the filaments,

any change in direction of traverse,

the yarn type and thickness,

the orientation of the needle with respect to the filaments,

the distorting effect of the (large) needle, and

the backing type,

to compensate for positional errors introduced by those factors.

Preferably the adjusting means comprises a design means which varies thelocation of the tufts in the pattern, a control means which varies thecontrol signals, or mechanical offsets in the traversing means andtufting head.

Preferably the design means defines the pattern by a series of vectorswhich represent either the length and direction of each row of tufts, orthe shape and size of each area of tufts.

Preferably the system includes means to calculate an integral number oftufts along the length of a line of tufts, which may be curved, from itsbeginning to its end.

Preferably the system includes means to calculate an integral number oflines across any area.

Preferably the system includes means to vary the spacing between lineson either side of, and parallel to, a boundary, between two areas,within predetermined tolerances, in order to ensure the line spacing atthe boundary remains within the predetermined tolerances.

Preferably the design means includes display means to display thepattern showing each row of tufts with their widths in scale with theirlengths.

Preferably the system includes means to check the pattern for anyoccurrences of localised tuft density falling outside predeterminedupper and lower limits.

Preferably the traversing means and tufting head cooperate to enable thehead to be pushed against the backing to cause any desired deflection ofthe backing.

Preferably the frame is mounted on the traversing means before tufting,and demounted from the traversing means once tufting has been completed.

Preferably the tufting head comprises:

a yarn feed mechanism which engages the yarn, in each reciprocation ofthe needle, to feed it to the needle as the needle descends after thetip of the needle has entered the backing but before the needle openingis completely clear of the backing, and disengages to stop feedingbefore the tip of the needle is clear of the backing;

an air feeder to pump a stream of air through the needle and entrain theyarn, and feed it through the needle; and

a yarn brake provided upstream of the yarn feed mechanism to preventadvance of the yarn when the feed mechanism is disengaged; wherein

the yarn feed mechanism comprises a pair of pinch wheels, at least oneof which is driven in rotation and has a portion of its peripheryarranged to engage the other wheel as it rotates, and a portion of itsperiphery arranged not to engage the other wheel as it rotates.

Interrupting the yarn drive in each reciprocation provides greaterreliability than known devices. This is because in the known devices theyarn is continuously advanced and can become entangled in the filamentsof the backing before they are fully parted. The intermittent drive alsoresults in greater consistency of pile height than is typical of knownmachines, since the beginning and end of each length of yarn isaccurately defined in embodiments of the invention. In addition theintermittent drive facilitates clean cutting of the yarn by allowing theyarn to be cut while it is stationary in some embodiments.

Preferably the head further comprises a yarn cutting device whichoperates to pass a blade through a transverse slot in the needle once inevery reciprocation at a time when the yarn is stationary and the needleis advancing toward the backing, to cut against an anvil placed at anacute angle to the blade.

Preferably the needle has an S-shaped profile.

Preferably the head further comprises a continuous disc-shaped foothaving a hole through which the needle reciprocates, the hole beingelongated behind the trailing edge of the needle.

Preferably the head further comprises a yarn blockage detector locatedbetween the yarn feed mechanism and the needle, to indicate divergenceor build-up of yarn, or both, in that region.

Preferably the head further includes a yarn change device comprising atube having a relatively narrow opening adjacent the yarn feedmechanism, and a relatively wide opening at its distal end, and air feedmeans selectively operable to direct a stream of air either from thewide to the narrow end of the tube to entrain yarn and feed it to theyarn feed mechanism, or from the relatively narrow to the wide end toeject yarn from the tufting head.

One of the problems with the known automated tufting heads is that themotor which drives the tufting head is mounted on the rotating parts ofthe head. Power and control signals must be fed to the motor by means ofa rotatable coupling. Slip rings have been found impractical since theyare bulky and unreliable in transmitting the control signals, and aspiral wound wire loom has been employed. The spiral loom introduces arestriction on a number of times the tufting head can rotate in a singledirection, and when the spiral is fully wound in one direction thetufting head is forced to change the direction of its rotation, whichcan result in a rotation through a much larger angle being required thanwould be necessary if a change in the direction rotation were notnecessary. The extra rotational movement costs valuable production time,and also may result in distortion of the tuft as the rotation of theneedle may pull the yarn. The spiral loom, as well as being expensive,is also prone to wire failures as a result of continual winding.

Preferably the system includes a reciprocating drive motor to drive theneedle in reciprocation, and a rotational drive motor to rotate theneedle about an axis, both mounted on a non-rotatable part of thetraversing means to supply drive to a rotatable part of the tufting headrespectively by means of a first drive wheel and a second drive wheelwhich are both mounted on the rotatable parts to be driven in rotationabout the axis; and wherein

in use, rotational drive of the first drive wheel is translated intoreciprocating motion of the needle and rotational drive of the seconddrive wheel directly causes rotation of the needle about the axis.

Where the tufting head comprises a forked blade mounted within theneedle for reciprocating motion, out of phase with the needle to locatethe yarn in the backing; then preferably, both the needle and the forkedblade are attached to respective tubes, both coaxial with an axis aboutwhich the needle is rotatable, both rotatable about that axis, and bothattached at their upper ends by means of rotatable couplings torespective carriages which are not rotatable about that axis but whichare both drivable in reciprocating motion to supply the reciprocatingmotion to the needle and blade.

These arrangements allow the tufting drive motor to be mounted on anon-rotating part of the tufting gun, and this reduces the rotationalmoment of inertia of the rotating part, which reduces the power and timerequired to move from one rotational position to another.

In known machines of the purely mechanical type the yarn takes acircuitous route through the mechanism which results in a friction dragload being applied to the yarn, which can cause the yarn to be damagedor even cut before the yarn brake is applied. This effect isparticularly prevalent at high speed operation, and in the knownmachines it is necessary to restrict the speed in order to ensure theyarn is not damaged. Therefore preferably the yarn is fed through a tubewhich is not rotatable about the axis, and which passes along the axisthrough both tubes to the needle.

BRIEF DESCRIPTION OF THE DRAWINGS

The method and system of the present invention will now be described, byway of example only, with respect to the accompanying drawings, inwhich:

FIG. 1 is a perspective view of a system for automatically tuftingfabrics embodying the present invention;

FIG. 2a is a schematic diagram illustrating the trajectory of a tuftingneedle during tufting, FIG. 2b is a plan view of a row of tufts tuftedby a needle following the trajectory of FIG. 2a, FIG. 2c is across-sectional view showing cut pile tufted by a needle following thetrajectory of FIG. 2a, and FIG. 2d is a cross-sectional view showingloop pile tufted by a needle following the trajectory of FIG. 2a;

FIG. 3 is a plan view showing the distortion of the backing when aneedle is inserted into it;

FIG. 4 is a plan view indicating the offset introduced by the distortionshown in FIG. 3;

FIG. 5a illustrates one way in which a design shape is interpreted bythe prior art, and FIG. 5b illustrates how the same design shape isinterpreted according to an embodiment of the invention;

FIG. 6a illustrates the location of tufts along a straight lineaccording to an embodiment of the invention, and FIG. 6b illustrates thelocation of tufts along a curved line according to an embodiment of theinvention;

FIG. 7 illustrates the application of the principles illustrated in FIG.6 to the design shape shown in FIG. 5;

FIG. 8 illustrates the application of the principles illustrated in FIG.6 to a different design shape;

FIG. 9a illustrates a potential row spacing problem, and FIG. 9billustrates the solution;

FIG. 10a illustrates another potential row spacing problem, and FIG. 10billustrates the solution;

FIG. 11 is a representation of a display from a design system embodyingthe invention;

FIG. 12 is an elevational view of a tufting head embodying the presentinvention;

FIG. 13 is an orthogonal elevation of the head of FIG. 12;

FIG. 14 is a detail from FIG. 13;

FIGS. 15a to m is a series of schematic diagrams showing the operationof the tufting head of FIGS. 12, 13 and 14 as it goes through a complete360° reciprocation;

FIG. 16 is a schematic diagram illustrating an alternative tufting headembodying the present invention;

FIG. 17 is an elevational view of another tufting head embodying thepresent invention; and

FIG. 18 is a detail from FIG. 16.

BEST MODES FOR CARRYING OUT THE INVENTION

Referring now to FIG. 1, an automatic tufting machine 1 comprises anupright metal frame 2. A first carriage 3 is arranged for horizontalmovement on frame 2. A second carriage 4 is arranged on the firstcarriage 3 for vertical movement. A mounting bracket 5 is attached tocarriage 4. Taken together, carriages 3 and 4 and mounting bracket 5comprise a traversing means in which a tufting head 6 is mounted.Tufting head 6 is mounted on a circular bearing for rotational movementabout an axis 7 extending perpendicular to the horizontal and verticaldirections mentioned. The tufting head is also arranged in mountingbracket 5 in a manner which permits it to advance towards the backing,and to be withdrawn from the backing, that is in the direction of axis7. The rotational movements of the tufting head, vertical movements ofcarriage 4 and horizontal movements of carriage 3 are achieved by use oftoothed belts which are driven by gears connected to servo motors. Theadvance and withdrawal of the tufting head is achieved by use of an airdriven slide.

Electrical power and, if required, compressed air are supplied totufting head 6. Yarn 8 is also supplied to the tufting head from a creel(not shown) during tufting.

In order to tuft, a backing 9 is stretched on a wooden frame 10 andsecured under tension over metal hooks 11. Frame 10 is then slid intoupper and lower rails, 12 and 13 respectively, on metal frame 2 where itis secured in the upright position shown.

A computer aided design system (CAD) is used to generate a design, and acomputer aided manufacturing system (CAM) is used to control the tuftingoperation. A pattern of tufts of different coloured yarns are stored asa data file in the computer aided design system. Control signals aredeveloped from this pattern by the computer aided manufacturing systemto control the horizontal and vertical movements of carriages 3 and 4,the rotational movements of tufting head 6, the degree of advance oftufting head 6 towards the backing 9, and the reciprocating movements ofa tufting needle, in tufting head 6, into and out of the backing.

When the backing has been completely tufted frame 10 is removed fromframe 2 to enable the application of a latex backing to the backing, andto release tufting machine 1 for further tufting using another stretchedframe 10.

During tufting, the tufting head 6 is pressed against the backing 9 atpreselected pressure to cause a desired deflection of the backing, andthe tip 14 (see FIG. 2a) of the hollow tufting needle 15 is pushed intoand out of the backing as the needle is reciprocated back and forth.

The needle tip 14 follows a near sinusoidal trajectory 16 through thebacking 9 as the tufting head traverses at a constant speed, and yarn isfed through the needle.

FIG. 2b is a plan view of the tufts 17 produced by the needle followingthe trajectory shown in FIG. 2a. If the material is cut at the bottom ofeach insertion of the needle through the backing, then a cut pile oflength h₁ is created as shown in FIG. 2c. Alternatively if the tuftingyarn is left uncut a loop pile of length h₂ is created as shown in FIG.2d.

There is another type of movement of the head, called a "move". In a"move" the tufting head is lifted from the backing and traversed to anew position without tufting. This facilitates accurate registration ofthe tufting head over the backing.

It has been found that, as the tufting head is traversed over thebacking, the tufts are inserted with positional errors in dependenceupon a number of factors and circumstances

Referring now to FIG. 3 the hollow needle 15 has a relatively largediameter when compared to the mesh size of the backing 9; the diameterof needle 15 can be seen to be equal to about five times the length ofthe spacing between filaments 18 of the undistorted backing. When needle15 is inserted into backing 9 the filaments are distorted as shown andthe distortion can be seen to extend through about sixteen filaments inthe horizontal and vertical directions.

The distortion causes no problem when the traverse is in the horizontalor vertical directions (that is the direction of the filaments) or indirections close to 45° between the horizontal and vertical, but whenthe direction of traverse is at other angles, for instance the angle 19shown, the distortion causes hole 20 to be the next hole entered ratherthan hole 21 which is the correct hole according to the theoreticaltrajectory. This introduces an error into the tuft positioning in adirection which depends on the direction of traverse.

In general the error causes the tufts to be located closer toward therespective axes than intended. The effect on rows of tufts isillustrated in FIG. 4 where the center line of the tufts 22 can be seento be offset from the needle trajectory 23 by an offset value 24.

Another source of tuft location error has been found to arise from thefact that the center of a tuft inserted into the backing lies somewherebetween the locations of the tip and the center of the tufting needle atthe instant the tip first penetrates the backing to sew that tuft. Thisresults in an error being introduced into the tuft location dependingupon the rotational orientation of the needle.

The degree of error introduced by these mechanisms is dependent, to someextent, on the yarn type and thickness, the distorting effect of thelarge diameter needle and the backing type.

Compensation may be effected by the CAD design system, for instance byadjusting the positions of the tufts to compensate for the errors once adesign has been finalised by the designer. Alternatively the CAD systemmay leave the design in the form finalised by the designer andcompensation may be introduced by the CAM control system which reads thedesign and then generates control signals which are sent to the tuftinghead. Another option is to incorporate compensations in the tufting headmechanism itself, for instance the needle can be turned slightly to picka different hole in the backing, or the rotational center of the headcan be adjusted so that the centers of the inserted tufts coincides withthe center of rotation. Another alternative would be to compensate bymeans of lookup tables.

Another problem which has been encountered is that it is difficult toproduce a fine and accurate pattern from relatively large tufts. Onemanner of arranging and inserting the tufts is to consider a pattern tobe a matrix 25 of tufts of different colours, each having a size 26 asshown in FIG. 5a (rather like the pixels of a picture displayed on avisual display unit). In this case to create any particular design shape27, all the tufts of a particular colour can be inserted in eitherhorizontal or vertical rows. In this case the resulting tufting patternis reduced to a series of straight line segments as shown by outline 28.In addition since the position of every tuft is defined in the matrix,there is a need for a very large amount of data which makes modificationof the design, such as changes in tuft lengths, very laborious anddifficult. A better way of defining the pattern is to define only thebeginning and end of each straight, 29 to 34, or curved, 35, line oftufts as shown in FIG. 5b, and to use an algorithm to calculate theposition of each individual tuft between the defined ends of each line.

With this type of compression the following instruction set

retract the head and move to position x₁, y₁

lower the head then sew to x₂, y₂

then retract the head and move to 0,0 can be represented in a data fileas:

    ______________________________________    X             Y     FUNCTION    ______________________________________    x.sub.1       y.sub.1                        MOVE    x.sub.2       y.sub.2                        SEW    0             0     MOVE    ______________________________________

A straight line algorithm then calculates the integer number of tuftsfor that line as follows:

the length of a line of tufts, from x₁ y₁ to x₂ y₂ is divided by thepreferred stitch length to give a theoretical number of stitches, andthis number is rounded to the nearest whole number. The stitch length isthen adjusted within a defined tolerance range to provide an integernumber of stitches along the length of the line. The positions of theresulting tufts 36 are shown in FIG. 6a.

Curves are defined by a series of data points x₃ y₃, x₄ y₄, x₅ y₅ and x₆y₆ (see FIG. 5b) and an indication of curve type, such as polynomial,spline, bezier etc. A curved line algorithm then calculates the integernumber of tufts for that curved line as before:

the length of the line, from x₃ y₃ to x₆ y₆ is divided by the preferredstitch lengths to give a theoretical number of stitches, and this numberis rounded to the nearest whole number. The stitch length is thenadjusted within a defined tolerance range to provide an integer numberof stitches along the length of the line. Again the positions of theresulting tufts 36 are shown

In both straight and curved lines the locations of the tufts may notcoincide with the positions of each data point. This is particularlynoticeable in the case of wavy lines where the curvature changes alongtheir length, because changes in curvature are accompanied by changes inthe spacing between the points defining the curve.

The rounding of the number of rows affects the density of the pile.Variations in density affect the compliance of the finished product,that is how much pressure it takes to distort the pile. In consequencedifferences in density effect the way the finished product feels totouch or walk on, and it also affects the way in which the pile sits,giving the finished product an inconsistent appearance. This problem maybe overcome by calculating the row spacing for a given area first, andthen calculating the tuft length for the rows of that area to give adensity of tufts between predetermined upper and lower limits.

The order of placement of tufts is important because when an area whichis surrounded by a vacant area is filled with tufts, the tufts candistort the backing and cause bulging in the edges of the tufted areawhich distorts the overall pattern. This can be compensated for to someextent by ensuring that two or three rows of tufts are inserted aroundthe edge of an area which is surrounded by a vacant area, before thecenter is filled.

Even better data compression can be achieved if the boundaries of eacharea are defined and algorithms are provided to calculate the row andstitch positions and spacings within each area. How this may be achievedwill now be described with reference to FIG. 7:

An area is defined by the data points x₇ y₇, x₈ y₈, x₉ y₉, x₁₀ y₁₀, x₁₁y₁₁, x₁₂ y₁₂, x₁₃ y₁₃, x₁₄ y₁₄, and x₁₅,y₁₅, and a number of otherparameters are provided. A first parameter, the perimeter offset 37, isused to calculate the start and end points of each line segment whichtogether make a perimeter 38 line of tufts centered just within theperimeter of the design shape. The perimeter offset provides definitionto the outline of the shape. Individual tuft positions along theperimeter line of tufts 38 are calculated for each line straight andcurved line as above.

The area inside the perimeter tufting is then filled by tuftingbackwards and forwards along lines 39 within the area. A number of otherparameters are required in order for the filling tuft positions to becalculated. These include row angle 40 and the fill offset 41. The rowspacing 42 and stitch length 43 are then calculated as indicated above.

FIG. 8 shows an alternative technique for filling an area. In this casethe outline of the area is defined by data points x₁₆ y₁₆, x₁₇ y₁₇, x₁₈y₁₈, x₁₉ y₁₉, x₂₀ y₂₀, x₂₁ y₂₁, and x₂₂ y₂₂. The curve type for thecurve between x₁₆ y₁₆ and x₂₀ y₂₀ is known, and the stitch length can becalculated for that row. Then the row spacing 44 is determined, and thestitch length for successive curved lines is calculated so that the areais filled ending at x₂₂ y₂₂.

The feature of ensuring constant density can be very usefully employedwhen generating a new pattern from an old pattern. For instance wherethe new pattern is merely a scaled version of an old pattern, once theareas are defined the filling of each area may be automaticallycalculated by the algorithm which ensures constant density.

Another type of problem which can arise is where one area is beingtufted adjacent to an area that has previously been tufted. Forinstance, referring to FIG. 9a, where all the rows in both areas areparallel, and tufting proceeds into a vacant corner bordered by thealready tufted area. In this case, if the rows of tufts approaching thealready tufted area are not correctly spaced with respect to the rows ofthe already tufted area, a gap 45 can be created between the two areaswhich is too narrow for an extra row; in other words the gap is lessthan twice the minimum row spacing allowable. This can lead to an areaof low tuft density, or at worst an obvious gap in the tufts. Theproblem may be overcome by adjusting the spacing between the rows,within specified tolerances, in either or both of the areas, see FIG.9b.

Another problem arises where an area having sides which are close to,but not parallel is required to be tufted. In this case if the area istufted by tufting rows parallel to one of the sides, gaps can occuralong one edge of the area where the rows meet as an angle, see FIG.10a. This problem can be overcome by fanning the rows so that a taperedgap is distributed across the area to be filled, see FIG. 10b. Thisresults in many small tapers between the rows, but no gaps are createdand the resultant variation in density can remain undetectable providingthe tolerance on row spacing is set with a suitable maximum.

When a pattern is being designed, say for a rug, some areas of thepattern may have shapes which cannot easily be generated by a set ofmathematical rules. In order to facilitate such design the CAD/CAMsystem is arranged to display the design by showing rows of tufts asbroad lines having the correct scaled width, see FIG. 11. This isparticularly useful where the tufts must be arranged in confined spacesbecause it allows the designer to ensure equal space on each side ofeach row thereby reducing the possibility of overtufting occurring. Thisalso allows a curved line of tufts to be shown as a series of straightrows having the required width, extending between the data points whichdefine the curve.

A further useful feature is to provide a zoom facility at onlypredetermined scaling, since this trains the designers to becomeaccustomed to seeing the patterns always at the same series of relativesizes.

The CAD/CAM system is advantageously arranged to allow a point in a rowof tufts to be moved, say by the operation of a mouse, and when a pointis moved the display shows the rows of tufts extending away from thatpoint automatically following the point by changing direction and lengthto accommodate the movement.

It is advantageous to include in the CAD/CAM system the ability to checkthe pattern by running through it, without tufting, to identify anypoints where lines or individual tufts either clash or become closerthan a specified tolerance to each other. An operator may then make adecision as to whether correction should be introduced into the pattern.

Referring now to FIGS. 12, 13 and 14, tufting head 100 comprises a base101 to which a needle 102 and a needle barrel 103 are mounted forvertical reciprocating motion. The needle 102 and barrel 103 are hollowand there is an opening in the bottom of the needle to allow yarn to befed out. A foot 104 is connected to base 101, and includes a holethrough which the needle may reciprocate.

A blade 105 for cutting the yarn is mounted on a carrier 106 which isattached to the end of a telescopic and rotatably mounted shaft 107. Thecarrier 106 is also connected to the needle barrel 103.

An electric motor 108 is mounted on the head. A series of drive belts,pulleys, differential gears, connecting rods and cranks, indicatedgenerally by 109, transfer rotating drive motion from the motor 108 intoreciprocating motion of the needle barrel 103 and shaft 107, androtating motion of blade carrier 106.

A compressed air supply is connected to a shroud 110 covering the upperend of the needle tube 103 to direct a stream of air down the hollowinterior and out of the opening in the bottom of the needle.

A pair of pinch wheels 111 and 112 are employed to feed yarn into theupper end of the needle tube 103. A yarn brake 113 is provided toprevent movement of the yarn when the pinch wheels are disengaged fromeach other.

FIG. 14 shows a sectional detail of needle barrel 103, the air supplyfrom shroud 110, and pinch wheels 111 and 112, together with theconstant drag yarn brake 113, and a length of yarn 114. One 111, of thepair of pinch wheels 111 and 112 is driven and has a portion of itsperiphery at a first, greater, radius R and a portion at a second,lesser, radius r. The relative sizes of the sectors of the wheel havingeach radius are selected and the rotational position of the wheel isselected to enable contact between the two pinch wheels over apreselected period of time during each revolution. When the pinch wheelsare in contact the yarn is gripped and driven downward. In this way theheight of the tufts, and the time during which yarn is driven downwardin each reciprocation of the needle can be controlled. This ensures thatthe yarn is only allowed to exit through the opening in the bottom ofthe needle when the backing filaments are fully parted.

In an alternative embodiment both pinch wheels have portions of greaterand lesser radius, and their relative rotational positions determine thelength of the yarn fed out and the timing relative to other operationsin the tufting sequence. In this case both wheels are driven and theirdrive shafts are geared together. The wheels can be adjusted andreclamped on the shafts at different rotational positions relative toeach other to produce different lengths of yarn, or to change thetiming.

The compressed air supply to the needle will be described. Thecompressed air is supplied to shroud 110 covering the upper end of theneedle barrel 103. The air enters an annular gallery 122 which runsaround the interior of the shroud 110, and exits through an angled slit123 which runs around the interior of the shroud 110. The slit 123 isangled to direct air downwards through the needle barrel 103. Thearrangement of the slit creates a vortex which is able to suck a looselength of yarn into the upper end of the needle barrel. Once the yarn isin the barrel, it is entrained in the air stream, held straight, anddirected downward through the barrel. Multiple slits may be provided inthe barrel, if desired.

The air jet exiting the opening in the bottom of the needle helps topart previously sewn tufts once the needle has penetrated the backing.This assists the sewing of new tufts without obstruction. Blockagesoccur from time to time when filaments of the backing and previouslysewn tufts obstruct the needle opening. The positioning of the shroud atthe upper of the needle barrel prevents the yarn being blown back out ofthe barrel when a blockage occurs in the needle. This is prone to happenwith prior art assemblies where the compressed air is supplied to thelower end of the needle barrel.

The yarn brake 113 is used to prevent the yarn being dragged into theneedle by the air jet when the pinch wheels 111 and 112 are not engaged.It also prevents the yarn being dragged out of the head by tension fromthe creel as the head traverses across the surface of the backing.

The yarn brake 113 consists of a channel section spring 125 loadedagainst a polished face 126. The yarn can be pulled out by the pinchwheels relatively easily, but can not be pulled back towards the creel.The spring 125 can be raised from the surface of the yarn when it isnecessary to pull back yarn from the needle, for instance when it isdesired to change yarns.

FIG. 15 illustrates the features of FIG. 14 together with a sectionalview of needle 102 and foot 104 as they move through a cycle ofoperation. At bottom dead center, in FIG. 15(a), a stitch 115 has justbeen located in the backing 116, and the needle is about to begin itsupward stroke. At this point in time the pinch wheels 111 and 112 arepulling a length of yarn 114 through the yarn brake 113 and the airsupply in shroud 110 is ON entraining the yarn neatly down the interiorof the needle barrel 103.

Later at (b), the needle 102 has risen and simultaneously the length ofyarn 114 has been drawn down.

At (c), the needle 102 has risen further and the length of yarn 114 hasbeen driven down further. Shortly after, the needle opening begins to beobstructed by the filaments of the backing closing across its upperedge.

At (d), the length of yarn 114 has reached its lowermost position andthe pinch wheels release the yarn. The first tuft of the stitch is nowin place.

The tip of the needle is subsequently drawn clear of the backing and theair supply is then turned OFF.

Just before (g), the rotating blade 105 begin to enter the needle barreland at (h), when the needle 102 has just passed top dead center thelength of yarn 114 is cut.

The tip of the needle enters the backing and at (i) the blade clears thetube.

At (j), the yarn begins feeding again as the descent of the needle 102pulls the upper end of the cut length of yarn 114 downwards.

Just before (k), the needle opening fully clears the filaments of thebacking and the air supply is switched ON again to hold the new lengthof yarn 117 straight. As the needle descends further the upper end ofthe cut length of yarn 114 is pulled down through the backing by theupper edge of the needle opening until, at bottom dead center the secondtuft of the stitch is fully located in the backing, and the stitch iscomplete.

The thin flexible blade 105 is mounted on the blade carrier 106 to entera transverse slot in the needle barrel 103 and to be drawn across thepolished face of an anvil. Both the face of the anvil and the edge ofthe blade are angled to reduce the contact area and increase thepressure at the instant of cutting. This reduces friction wear and heatgeneration.

The intermittent yarn drive results in the yarn being held stationary atthe time the blade 105 is cutting. The needle 102 on the other hand isat this time moving towards the backing. This means that the yarn ispulling the blade back against the anvil during the cutting operation,and as a consequence minimal blade preload is required against theanvil. The timing of the cut can be adjusted to cause the leading andtrailing ends of each length of yarn to be varied every time the stitchlength is changed.

A semi-automatic yarn changer may be incorporated into the head. Such ayarn changer includes a barrel having a narrow end adjacent the pinchwheels 111 and 112, and a wide distal end. At least two annular airgalleries with air outlet slits are provided near the distal end of theyarn changer. A first to generate a stream of air downward through thechanger and to entrain a loose end of yarn and feed it down through thebarrel to the yarn pinch wheels. And a second to eject a length of yarnfrom the barrel.

In operation, to change yarn the head is moved to the position in itscycle where the blade 105 is clear of the barrel, the needle air streamis OFF, and the pinch wheels are apart. The yarn brake is disengaged andthe second air stream turned ON to cause a stream of air to flow up thebarrel of the yarn changer and eject the length of yarn in the head.Then the second air stream is turned OFF, the first air stream and theneedle air stream turned ON, and the end of a new length of yarn isbrought near the distal end. The new end is captured by a vortex createdby the first air stream and fed down the barrel so it is eventuallyentrained by the needle air stream. The yarn brake is then lowered andthe head is thereafter able to continue its cycle.

In FIG. 16 an embodiment of the tufting head will be described in whichboth the tufting drive motor 108 and the motor 127 for providingrotational movement of the tufting head are mounted on a part of thetufting head which does not rotate. Drive from the tufting drive motoris supplied to the rotating part of the tufting head by means of atoothed belt 128 which turns a first drive wheel 129 which in turndrives differential gears, and a connecting rod and crank, indicatedgenerally by 130 in order to transfer reciprocating motion to the needle102.

Rotational drive is applied to the tufting head from motor 127 bytoothed belt 131 which turns a second drive wheel 132 which is directlycoupled to the rotatable part of the tufting head.

At the end of each row of tufts, the needle rotation motor 127 is drivento its new position so that the needle is facing inn the correctdirection for the next row of tufts. Since this motion would causemovement of toothed belt 128 supplying drive to the tufting head, drivemotor 108 is arranged to be driven to a compensating amount in order toensure the needle remains at the correct part of its cycle.

A purely mechanical tufting head will now be described with reference toFIG. 17 and 18. A forked rod 133 is reciprocally mounted within hollowneedle 102, which is usually of U-shaped cross-section rather than beingtubular, and the yarn is located in the fork at the end of rod 133. Rod133 is mounted on a slidable carriage 134 for reciprocal motion guidedby a slide 135 which runs along guide rod 136. A first tube 137 extendsup from carriage 134 to a second slide 138 and this slide is driven upand down by an eccentric drive 139 from a rotational drive input. Secondslide 138 is guided in its up and down movement by guide rods 140 and141.

The needle 102 is driven up and down in a reciprocating motion by aconnecting rod 142 which is connected to a third slide 143 which alsorides up and down along guide rod 136. A second tube 144 extends upwardsfrom slide 143 to a fourth slide 145 which is driven up and down byeccentric 146 driven by the same rotational drive as eccentric 139, but180° out of phase with it. Slide 145 is also guided in its up and downmovement by guide rods 140 and 141. Both first tube 137 and second tube144 are hollow and coaxial, with first tube 137 extending within secondtube 144.

The yarn is supplied through the hollow interior of yarn tube 147 whichextends coaxially in a straight line through the hollow interior offirst tube 137.

Tubes 137 and 144 are rotatably retained in their respective upperslides 138 and 145 by respective rotational bearings 148 and 149, andguide rod 136 is rotatable with respect to guide rods 140 and 141 abouta vertical axis by means of rotational bearing 150. A detailed view ofthe arrangement is shown in FIG. 18. Rotational drive is supplied toguide rod 136 by means of toothed belt 151 to rotate it and slides 135and 143 in order to turn the needle 102, foot 104 and forked rod 133with respect to the remainder of the head, while at the same timereciprocating up and down motion is supplied. Yarn tube 147 does notrotate and keeps the yarn straight and free from twists.

A camming surface 152 on carriage 134 operates a lever 153 to brake theyarn, if required, at the correct point in every cycle so that theforked rod 133 can cut the yarn to make cut pile. A solenoid operatedyarn break 154 is used at the end of a section of loop pile; when a looppile is being made the cam brake is disabled, and a blunt forked rod 133is usually employed in order to prevent the yarn being damaged at anypoint in the cycle.

With the purely mechanical type of head overtufting can be achieved sothat, for instance, a carpet can be embroidered with a customiseddesign.

It should be appreciated that, although the invention has been describedwith reference to particular embodiments it could be embodied in otherforms.

What is claimed is:
 1. A method of automatically tufting fabrics,comprising the steps of:(a) stretching a backing fabric consisting of aplurality of filaments over a frame so that the filaments form a gridnetwork with the filaments extending in at least two directions; (b)traversing a tufting head over the backing under the influence ofcontrol signals, and reciprocating a needle in the tufting head into andout of the backing at a rate related to a speed of traverse of thetufting head, to insert tufts of yarn into positions in the grid networkof the backing in accordance with a preselected pattern of tufts; (c)determining a distorting effect the needle has on the grid network wheninserted into the backing, and (d) adjusting actual positions of theneedle on the grid network relative to the positions of the tufts in thepreselected pattern, to compensate for positional errors introduced bythe distorting effect the needle has on the grid network.
 2. A method ofautomatically tufting fabrics according to claim 1, wherein the step ofadjusting comprises at least one of varying the locations of the tuftsin the predetermined pattern, varying the control signals, andmechanically compensating the traversing and tufting head mechanisms. 3.A method of automatically tufting fabrics according to claim 1, furthercomprising a step of adjusting the actual positions of the needlerelative to the positions of the tufts in the pattern, in dependence onthe distance between the position of a tuft center, and where the needletip begins to enter the backing in order to sew that tuft.
 4. A methodof automatically tufting fabrics according to claim 1, in which thepredetermined pattern is defined by vectors which represent at least oneof the length and direction of each row of tufts, and the shape and sizeof each area of tufts.
 5. A method of automatically tufting fabricsaccording to claim 1, comprising the step of calculating an integralnumber of tufts along the length of a line of tufts, which may becurved, from its beginning to its end.
 6. A method of automaticallytufting fabrics according to claim 1, comprising the step of calculatingan integral number of lines across any area Of the backing.
 7. A methodof automatically tufting fabrics according to claim 1, comprising thestep of varying the spacing between lines on either side of and parallelto a boundary between two areas of the backing, within predeterminedtolerances, in order to maintain row spacing at the boundary within thepredetermined tolerances.
 8. A method of automatically tufting fabricsaccording to claim 1 comprising, where an area of the backing has twotapering boundaries, the step of tufting rows in a tapered formationbetween the two boundaries to share an equal proportion of the taperbetween each adjacent pair of rows.
 9. A method of automatically tuftingfabrics according to claim 1, comprising the steps of calculating anintegral number of tufts along any given row in dependence on a spacingbetween that row and immediate adjacent rows in order to ensure that atuft density remains within predetermined upper and lower limits.
 10. Amethod of automatically tufting fabrics according to claim 1, comprisingthe step of displaying the pattern as a diagram showing arranged rows oftufts, wherein the displayed pattern shows the tufts with their widthsin scale with their lengths.
 11. A method of automatically tuftingfabrics according to claim 1, comprising the step of checking thepattern for any occurrences of localised tuft density falling outsidepredetermined upper and lower limits.
 12. A method of automaticallytufting fabrics according to 1, comprising the step of pressing thetufting head against the backing during tufting at a preselectedpressure to cause a desired deflection of the backing.
 13. A method ofautomatically tufting fabrics according to claim 1, including the stepof mounting the frame onto a machine which includes means for traversingthe tufting head over the backing, before tufting, and dismounting theframe from the machine once tufting has been completed.
 14. A system forautomatically tufting fabrics, comprising:(a) a frame over which, inuse, a backing fabric consisting of a plurality of filaments is attachedso that the filaments form a grid network with the filaments extendingin at least two directions; (b) traversing means to traverse a tuftinghead over the backing under influence of control signals; (c) a tuftinghead mounted in the traversing means and having a tufting needle able toreciprocate into and out of the backing, at a rate related to a speed oftraverse of the tufting head, to insert tufts of yarn into positions inthe grid network of the backing in accordance with a preselected patternof tufts; (d) means for determining a distorting effect the needle hason the grid network when inserting into the backing; and (e) adjustingmeans to adjust the actual positions of the needle on the grid networkrelative to the positions of the tufts in the predetermined pattern tocompensate for positional errors introduced by the distorting effect.15. A system according to claim 14, wherein the adjusting meanscomprises at least one of the following: a design means to vary thelocation of the tufts in the pattern, a control means to vary thecontrol signals, and means for mechanically compensating the traversingmeans and tufting head.
 16. A system according to claim 14, wherein theadjusting means comprises a design means to vary the location of thetufts in the pattern, the design means adapted to define the pattern bya series of vectors which represent either one of the length anddirection of each row of tufts, and the shape and size of each area oftufts.
 17. A system according to claim 14, further comprising means tocalculate an integral number of stitches along a length of a line oftufts, which may be curved, from its beginning to its end.
 18. A systemaccording to claim 14, further comprising means to calculate an integralnumber of lines across any area of the backing.
 19. A system accordingto claim 14, further comprising means to vary a spacing between lines oneither side of and parallel to a boundary, between two areas of thebacking, within predetermined tolerances, in order to ensure that linespacing at the boundary remains within the predetermined tolerances. 20.A system according to claim 14, further comprising means to enable rowsto be tufted between tapering boundaries of an area of the backing in atapered formation so that an equal proportion of the taper between thetwo boundaries is shared between each pair of rows.
 21. A systemaccording to claim 14, further comprising means to calculate an integernumber of tufts along any given row in dependence on a spacing betweenthat row and its immediate adjacent rows in order to ensure that tuftdensity does not fall outside predetermined upper and lower limits. 22.A system according to claim 15, wherein the design means includesdisplay means to display the pattern showing each row of tufts withtheir widths in scale with their lengths.
 23. A system according toclaim 14, further comprising means for checking the pattern for anyoccurrences of localized tuft density falling outside predeterminedupper and lower limits.
 24. A system according to claim 14, furthercomprising means for enabling the traversing means and tufting head tocooperate so that the tufting head can be pushed against the backingsuch as to cause any desired deflection of the backing.
 25. A systemaccording to claim 14, wherein the traversing means comprises a furtherframe on which the frame holding the backing is mounted before tufting,and demounted once tufting has been completed.
 26. A system according toclaim 14, wherein the tufting head comprises:a yarn feed mechanism whichengages a yarn to be tufted, in each reciprocation of the needle, tofeed the yarn to the needle as the needle descends after a tip of theneedle has entered the backing but before a needle opening is completelyclear of the backing, and disengages to stop feeding before the tip ofthe needle is clear of the backing; an air feeder to pump a stream ofair through the needle and entrain the yarn, and feed it through theneedle; and a yarn brake provided upstream of the yarn feed mechanism toprevent advance of the yarn when the feed mechanism is disengaged;wherein the yarn feed mechanism comprises a pair of pinch wheels, atleast one of which is driven in rotation and has a portion of itsperiphery arranged to engage the other wheel as it rotates, and aportion of its periphery arranged not to engage the other wheel as itrotates.
 27. A system including a tufting head according to 26, furtherincluding a yarn change device comprising a tube having a relativelynarrow opening adjacent the yarn feed mechanism, and a relatively wideopening at its distal end, and air feed means selectively operable todirect a-stream of air either from the wide to the narrow end of thetube to entrain yarn and feed it to the yarn feed mechanism, or from therelatively narrow to the wide end to eject yarn from the tufting head.28. A system according to claim 14, wherein a reciprocating drive motorto drive the needle in reciprocation, and a rotational drive motor torotate the needle about an axis are both mounted on a non-rotatable partof the traversing means and supply drive to a rotatable part of thetufting head respectively by means of a first drive wheel and a seconddrive wheel which are both mounted on the rotatable parts to be drivenin rotation about the axis; and whereinin use, rotational drive of thefirst drive wheel is translated into reciprocating motion of the needleand rotational drive of the second drive wheel directly causes rotationof the needle about the axis.
 29. A system according to claim 14,wherein the tufting head comprises a forked blade mounted within theneedle for reciprocating motion, out of phase with the needle to locatethe yarn in the backing;wherein both the needle and the forked blade areattached to respective tubes, both coaxial with an axis about which theneedle is rotatable, both rotatable about that axis, and both attachedat their upper ends by means of rotatable couplings to respectivecarriages which are not rotatable about that axis but which are bothdrivable in reciprocating motion to supply the reciprocating motion tothe needle and blade.
 30. A system according to claim 29, wherein theyarn is fed through a tube which is not rotatable about the axis, andwhich passes along the axis through-both tubes to the needle.
 31. Amethod of automatically tufting fabrics according to claim 1, comprisingthe step of determining at least one of the following factors:adirection of traverse of the tufting head with respect to the filaments;any change in the direction of traverse; the type of yarn and itsthickness; a rotational orientation of a pointed lower end of the needlewith respect to the filaments; the backing; and adjusting the actualposition of the needle on the grid network relative to the positions ofthe tufts in the preselected pattern to compensate for any positionalerrors introduced by the above factors.
 32. A method of automaticallytufting fabrics, comprising the steps of:(a) stretching a backing fabricover a frame to form a grid network of filaments extending in at leasttwo directions; (b) traversing a tufting head over the backing under theinfluence of control signals, and reciprocating a needle in the tuftinghead into and out of the backing at a rate related to a speed oftraverse of the tufting head, to insert tufts of yarn into the backingin accordance with a preselected pattern of tufts; (c) determining atleast one of the following factors:a direction of traverse of thetufting head with respect to the filaments, any change in the directionof traverse, the yarn type and thickness, a rotational orientation of atip of the needle with respect to the filaments, a distorting effect theneedle has on the grid network of filaments when inserted into thebacking, and the backing; (d) adjusting the positions of the needle onthe grid network relative to the positions of the tufts in thepreselected pattern to compensate for positional errors introduced bythe factors determined in (c); and (e) adjusting the positions of theneedle on the grid network relative to the positions of the tufts in thepattern, in dependence of the distance between the position of a tuftcenter and the position where the needle tip begins to enter the backingin order to sew that tuft.
 33. A method of automatically tuftingfabrics, comprising the steps of:(a) stretching a backing fabric over aframe to form a grid network of filaments extending in at least twodirections; (b) traversing a tufting head over the backing under theinfluence of control signals, and reciprocating a needle in the tuftinghead into and out of the backing at a rate related to a speed oftraverse of the tufting head to insert tufts of yarn into the backing inaccordance with a preselected pattern of tufts; (c) determining at leastone of the following factors:a direction of traverse of the tufting headwith respect to the filaments, any change in the direction of traverse,the yarn type and thickness, a rotational orientation of a tip of theneedle with respect to the filaments, a distorting effect the needle hason the grid network of filaments when inserting into the backing, andthe backing; (d) adjusting the positions of the needle on the gridnetwork relative to the positions of the tufts in the preselectedpattern to compensate for positional errors introduced by the factorsdetermined in (c); and (e) varying the spacing between lines on eitherside of and parallel to a boundary between two areas of the backingwithin predetermined tolerances, in order to maintain row spacing at theboundary within the predetermined tolerances.
 34. A method ofautomatically tufting fabrics comprising the steps of:(a) stretching abacking fabric over a frame to form a grid network of filamentsextending in at least two directions; (b) traversing a tufting head overthe backing under the influence of control signals, and reciprocating aneedle in the tufting head into and out of the backing at a rate relatedto a speed of traverse of the tufting head, to insert tufts of yarn intothe backing in accordance with a preselected pattern of tufts to form atufted fabric; (c) determining at least one of the following factors:adirection of traverse of the tufting head with respect to the filaments,any change in the direction of traverse, the yarn type and thickness, arotational orientation of a tip of the needle with respect to thefilaments, a distorting effect the needle has on the grid network offilaments when inserted into the backing, and the backing; (d) adjustingthe positions of the needle on the grid network relative to thepositions of the tufts in the preselected pattern to compensate forpositional errors introduced by the factors determined in (c); and (e)where an area of the tufted fabric has two tapering boundaries, tuftingrows in a tapered formation between two boundaries to share an equalproportion of taper between each adjacent pair of rows.
 35. A method ofautomatically tufting fabrics, comprising the steps of:(a) stretching abacking fabric over a frame to form a grid network of filamentsextending in at least two directions; (b) traversing a tufting head overthe backing under the influence of control signals, and reciprocating aneedle in the tufting head into and out of the backing at a rate relatedto a speed of traverse of the tufting head, to insert tufts of yarn intothe backing in accordance with a preselected pattern of tufts; (c)determining at least one of the following factors:a direction oftraverse of the tufting head with respect to the filaments, any changein the direction of traverse, the yarn type and thickness, a rotationalorientation of a tip of the needle with respect to the filaments, adistorting effect the needle has on the grid network of filaments wheninserted into the backing, and the backing; (d) adjusting the positionsof the needle on the grid network relative to the positions of the tuftsin the preselected pattern to compensate for positional errorsintroduced by the factors determined in (c); and (e) calculating anintegral number of tufts along any given row in dependence on thespacing between that row and its immediately adjacent rows in order toensure the tuft density remains within predetermined upper and lowerlimits.
 36. A method of automatically tufting fabrics, comprising thesteps of:(a) stretching a backing fabric over a frame to form a gridnetwork of filaments extending in at least two directions; (b)traversing a tufting head over the backing under the influence ofcontrol signals, and reciprocating a needle in the tufting head into andout of the backing at a rate related to a speed of traverse of thetufting head, to insert tufts of yarn into the backing in accordancewith a preselected pattern of tufts; (c) determining at least one of thefollowing factors:a direction of traverse of the tufting head withrespect to the filaments, any change in the direction of traverse, theyarn type and thickness, a rotational orientation of a tip of the needlewith respect to the filaments, a distorting effect the needle has on thegrid network of filaments when inserted into the backing, and thebacking; (d) adjusting the positions of the needle on the grid networkrelative to the positions of the tufts in the preselected pattern tocompensate for positional errors introduced by the factors determined in(c); and (e) displaying the predetermined pattern as a diagram showingarranged rows of tufts, wherein displayed tufts show their widths inscale with their lengths.
 37. A method of automatically tufting fabrics,comprising the steps of:(a) stretching a backing fabric over a frame toform a grid network of filaments extending in at least two directions;(b) traversing a tufting head over the backing under the influence ofcontrol signals, and reciprocating a needle in the tufting head into andout of the backing at a rate related to a speed of traverse of thetufting head, to insert tufts of yarn into the backing in accordancewith a preselected pattern of tufts; (c) determining at least one of thefollowing factors:a direction of traverse of the tufting head withrespect to the filaments, any change in the direction of traverse, theyarn type and thickness, a rotational orientation of a tip of the needlewith respect to the filaments, a distorting effect the needle has on thegrid network of filaments when inserted into the backing, and thebacking; (d) adjusting the positions of the needle on the grid networkrelative to the positions of the tufts in the preselected pattern tocompensate for positional errors introduced by the factors determined in(c); and (e) checking the predetermined pattern for any occurrences oflocalized tuft density falling outside predetermined upper and lowerlimits and modifying the pattern to compensate therefor.
 38. A method ofautomatically tufting fabrics, comprising the steps of:(a) stretching abacking fabric over a frame to form a grid network of filamentsextending in at least two directions; (b) traversing a tufting head overthe backing under the influence of control signals, and reciprocating aneedle in the tufting head into and out of the backing at a rate relatedto a speed of traverse of the tufting head, to insert tufts of yarn intothe backing in accordance with a preselected pattern of tufts; (c)determining at least one of the following factors:a direction oftraverse of the tufting head with respect to the filaments, any changein the direction of traverse, the yarn type and thickness, a rotationalorientation of a tip of the needle with respect to the filaments, adistorting effect the needle has on the grid network of filaments wheninserted into the backing, and the backing; (d) adjusting the positionsof the needle on the grid network relative to the positions of the tuftsin the preselected pattern to compensate for positional errorsintroduced by the factors determined in (c); and (e) pressing thetufting head against the backing during tufting at a preselectedpressure to cause a desired deflection of the backing.